/*
 *  Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "ns_fft.h"

#include "fft4g.h"

namespace webrtc {

    NrFft::NrFft() : bit_reversal_state_(kFftSize / 2), tables_(kFftSize / 2) {
        // Initialize WebRtc_rdt (setting (bit_reversal_state_[0] to 0 triggers
        // initialization)
        bit_reversal_state_[0] = 0.f;
        std::array<float, kFftSize> tmp_buffer{};
        tmp_buffer.fill(0.f);
        WebRtc_rdft(kFftSize, 1, tmp_buffer.data(), bit_reversal_state_.data(),
                    tables_.data());
    }

    void NrFft::Fft(rtc::ArrayView<float, kFftSize> time_data,
                    rtc::ArrayView<float, kFftSize> real,
                    rtc::ArrayView<float, kFftSize> imag) {
        WebRtc_rdft(kFftSize, 1, time_data.data(), bit_reversal_state_.data(),
                    tables_.data());

        imag[0] = 0;
        real[0] = time_data[0];

        imag[kFftSizeBy2Plus1 - 1] = 0;
        real[kFftSizeBy2Plus1 - 1] = time_data[1];

        for (size_t i = 1; i < kFftSizeBy2Plus1 - 1; ++i) {
            real[i] = time_data[2 * i];
            imag[i] = time_data[2 * i + 1];
        }
    }

    void NrFft::Ifft(rtc::ArrayView<const float> real,
                     rtc::ArrayView<const float> imag,
                     rtc::ArrayView<float> time_data) {
        time_data[0] = real[0];
        time_data[1] = real[kFftSizeBy2Plus1 - 1];
        for (size_t i = 1; i < kFftSizeBy2Plus1 - 1; ++i) {
            time_data[2 * i] = real[i];
            time_data[2 * i + 1] = imag[i];
        }
        WebRtc_rdft(kFftSize, -1, time_data.data(), bit_reversal_state_.data(),
                    tables_.data());

        // Scale the output
        constexpr float kScaling = 2.f / kFftSize;
        for (float &d : time_data) {
            d *= kScaling;
        }
    }

}  // namespace webrtc
